The overall objective of the proposed research is to determine the role of specific viral genes in the expression and maintenance of the transplantation rejection antigen (TrAg) in cells infected with or transformed by papovavirus SV40. We have recently shown that a functional A gene product, which is known to be involved in the initiation and maintenance of cell transformation, is required for the expression of TrAg. We now propose to further explore the role of the viral genome in the expression of TrAg by investigating: (1) The expression of TrAg in permissive cells infected with mutants of SV40 and relationship to the map location of the mutants. (2) Expression of TrAg in tsA transformed cells and its relationship to various parameters of the transformed cell phenotype. (3) The relationship of TrAg to the A protein and to T antigen. (4) The nature of TrAg cell surface receptors. (5) Cross-reactivity between SV40 TrAg and TrAg in cells transformed by human papovaviruses. A determination of the role of SV40 genes in the expression and maintenance of TrAg and of the interaction of this antigen with the cell surface is of considerable importance in expanding understanding of viral oncogenesis and immunosurveillance mechanisms which mediate the elimination of potential tumor cells.